I like my Smiths... For just about all of the reasons listed above. Balancing the collection is a good one, they simply can fire loads autos can't and acheive ballistics similar calibres in autos can't due to the ability to use slow powders. 10mm is *kind* of an exception, it is sort of a standard semi auto pistol magnum round capable of using slow powders quite efficiently, and thus can lie between the .357 and .41 magnums in terms of power with many loads.
For instance, the 9mm on average can get 1250+ fps velocity with +P ammo and 124gr. bullets. The .357 can too using similar fast powders and 125gr. bullets, BUT the .357 can also use slower powders and drive those same bullets to in excess of 1600fps, and all this considering similar barrel lengths and the fact the bullet is the same size and weight!
Then you have versatility... Running specials in magnums, and some of the large bores like the .460 can run a few different calibres. Smith is also making all kinds of new revolvers in all kinds of materials. I have a 686+ 6", one of my favorites but big and heavy, a 340PD that is 12oz. with five shots .357 and small and super light, and my wife has a shrouded hammer 649 5 shot .357. They make something for everyone, and I'd like their scandium/titanium .44mag. You can get 'em in all calibres, even auto calibres and with moon clips --have you ever seen Jerry Miculek reload a revolver? He can shoot an 8 shot Smith revolver like a machinegun accurately and reload it faster than I can any auto pistol or rifle. Amazing. They are most definitely still applicable in every way today, from competition, to defense, to combat, to hunting, to fun at the range. In a lot of ways, Smith and Wesson has kept the technology up to keep up with autos in a lot of way as to keep them relevant well into the future.
I would like to see some new revolvers chambered in some of the new short rifle rounds though, perhaps even the 6.5 Grendel or .224BOZ (or even a .44mag necked down to a 6.5mm bullet with a 6" plus barrel). This would be a new leap foward in revolver technology if you ask me.
Also interesting to point out regarding relevance of revolvers today is that .500 S&W mag revolver with the 8" + barrel has ballisitics similar to the .50 Beowulf AR carbine in 16" with several loads. Pretty interesting.
I been collecting them for years, autos and revolvers, and the last revolver was bought for my wife just a couple of weeks ago. I'm currently looking for a PSL, a Smith 10mm auto, and a 329PD, all at good prices either new or almost new, in addition to the projects I have in the works. So revolvers are definitely relavent for me.